Note: Descriptions are shown in the official language in which they were submitted.
! 2l~08~3
AQUEOU5, R~r!RN~r T Y ENUL5IFIED
~t Rvr~ RE5IN DI8PERSION5
Baak~ro~n~'l of th~ Invention
Field of the Tnvention
5 The invention relates to agueous, externally
emulsified acrylate resin dispersions comprising
hydrophilic polyesters as emulsifiers, processes for
their preparation, and to their use, for example, in
water-dilutable stoving clearcoats and solid-color
stoving topcoats and to two-component systems which can
be employed at temperatures between room temperature and
stoving temperatures.
Description of Rol ~ted ~rt
Acrylate resins as binders in coating materials are
known, for example, from DE-A 29 42 327 and
EP-A 0 056 971. The coating materials produced
therewith, however, contain solvent. Water-dilutable
autoemulsified acrylate resins which can be employed in
aqueous topcoats are described, for example, in
DE-A 40 09 031 and EP-A 0 619 329. The coating
materials, however, contain auxiliary solvents which are
miscible with water and which pass into the d~ re by
evaporation on drying or stoving. In the case of
relatively thick coats of coatings produced from such
coating materials, surface defects appear, so-called boil
marks. For technical and environmental reasons it is
desirable to reduce the solvent content in coating
materials or even to provide completely solvent-free
coating materials. In particular for the so-called
basecoat-clearcoat process in the f;n;~h;n~ of auto-
mobiles it is desirable to use an aqueous clearcoat
comprising little or no solvent.
` 218~3
--
--2--
ry of the Tnv~n~; on
An object of the invention, therefore, was to
provide acrylate resin dispersions which can be used in
binders and which can be applied even in relatively thick
5 coats without surface defects.
It was also an object of the invention to provide a
method of using and a method for making such acrylate
resin dispersions.
In accordance with these objectives, there has been
10 provided in accordance with a first aspect of the inven-
tion, an aqueous acrylate resin dispersion comprising
mass fractions, in the solid, of (A) from 5 to 50% of a
hydrophilic polyester ~ n~nt and (B) from 95 to 50% of
an acrylate copolymer containing at least one hydroxyl
15 group and at least one acid group.
In accordance with these objectives, there are also
provided according to other aspects of the invention
various uses for the dispersions in, for example, aqueous
stoving enamels, such as aqueous stoving clearcoats and
20 aqueous solid-color stoving topcoats, as well as in
aqueous two-component binder systems.
Further objects, features, and advantages of the
invention will become apparent from the detailed
description of preferred embodiments that follows.
De~ d Description of the ~referr~:d ~-nho~;r^nts
It has been found by the present inventors that
externally emulsified acrylate resin dispersions with
hydroxyl groups and acid groups in the acrylate copolymer
and with a hydrophilic polyester as emulsifier,
30 optionally in combination with appropriate crosslinking
agents, achieve the objects mentioned above.
The invention provides aqueous stoving enamels,
i . e., aqueous stoving clearcoats and aqueous solid-color
stoving topcoats, wherein the binders employed are
35 aqueous, solvent-free or low-solvent dispersions of
acrylate resins containing hydroxyl groups and acid
2~8~
--3
groups, with hydrophilic polyesters being used as
emulsifiers.
The invention additionally provides aqueous
two-component binder systems comprising acrylate resin
5 dispersions according to the invention.
The term low-solvent in the context of this inven-
tion is used to refer to those dispersions having a mass
fraction of not more than 20%, preferably up to 15%, of
solvents, the solvents being water-miscible solvents.
The invention provides aqueous acrylate resin
dispersions, the solids of which comprise mass fractions
of
(A) from 5 to 50% of a hydrophilic polyester component
and
15 (B) from 50 to 95% of acrylate resin containing hydroxyl
groups and acid groups which are partially or
completely neutralized.
The mass fraction of solids in the dispersion is, in
accordance with the invention, generally from 10 to 70%,
20 preferably from 20 to 60% and, with particular
preference, from 30 to 50%. In the low-solvent
~;~q~Pr~ nq the L- inSPr includes a mixture of water and
one or more water-miscible solvents. In the case of the
preferred solvent-free dispersions, the L~ ;n~lPr merely
25 includes water.
The invention also provides the method of use of
hydrophilic polyesters (A) which are employed as
emulsifiers in the dispersions according to the
invention. It is also possible to use mixtures of
3 0 hydrophilic polyesters according to (A) . The hydrophilic
nature of the polyesters is achieved in any desired
manner, for example, by use of mass fractions of from l
to 20%, based on the sum of the amounts of substance of
the polyester precursors, of ionic or ionogenic or
35 nonionic hydrophilic structural units.
To prepare the polyesters it is preferred to employ
mole fractions of from 3 to 15%, particularly preferably
from 5 to 13%, of hydrophilic structural units. Suitable
ionic structural units include those which, in addition
2~Q~l~
--4--
to the functional groups required for polycondensation
(hydroxyl and acid groups, preferably carboxylic acid
groups), also have ionic groups, i . e., cationic or
anionic groups, or which comprise structures which are
5 able to form such ionic groups. Examples include acid
groups such as carboxyl, sulfonic acid, sulfinic acid,
phosphonic acid and phosphinic acid groups, and cation-
f orming groups, such as phosphine groups and amino
groups, preferably tertiary amino groups, and the ionic
10 groups which are obtainable from these groups by reaction
with bases or acids or quaternization agents, for
example, methyl iodide.
By incorporating nonionic hydrophilic groups, for
example, polyoxyalkylene ether segments whose alkylene
15 groups, are selected from ethylene and propylene groups
and mixtures thereof, it is possible to prepare nonionic
hydrophilic polyesters which are likewise suitable for
the invention.
The polyesters of the invention are preferably
20 purely aliphatic polyesters whose polyester-forming
structural units therefore consist exclusively of
aliphatic hydroxyl ,- _ c and aliphatic organic acids
and/or their esters or anhydrides. The aliphatic
hydroxyl compounds and acids and/or their esters or
25 anhydrides may be linear, branched, or cyclic.
Preference is given to polyesters of dibasic acids and
dihydroxyaliphatic compounds, it also being possible for
up to 10% of the quantities of dibasic acids and
dihydroxy compounds to be replaced by tribasic or higher
30 polybasic acids and/or by compounds having three or more
hydroxyl groups. A preferred range for the amount of
substance of trifunctional compounds is from 1 to 5%. It
is also preferred, in the case of higher contents (over
3 mol per 100 mol) of trifunctional compounds, also to
35 add monobasic acids and/or monohydroxy compounds with
amounts of substances of in each case up to 396 based on
the sum of the quantities of acids and/or hydroxyl
compounds, in order to place an upper limit on the molar
~asses of the polyesters prepared in this way.
~ 2180~3
--5--
While the polyesters (A) may be prepared as desired,
they are preferably prepared from the hydroxy c, llnrls
and the acids with the addition of compounds which are
known as esterification catalysts. Suitable compounds
5 include Bronsted and Lewis acids and bases, and also
oxides and salts of metals of the main groups and
subgroups of the periodic table.
The hydrophilic structural units can in this case
also be esterified provided they do not adversely affect
10 the polycondensation. For example, polyoxyalkylene ether
glycols can be included for use in the condensation.
When dihydroxy acids such as dimethylolpropionic acid or
dillydr vxy:,uccinic acid are used as ionogenic structural
unit it is preferred, on the other hand, to react the
15 preformed polyester with these ionogenic c--mro~ln~C under
ester-forming conditions.
Instead of the acids and hydroxy compounds it is
also possible to employ ester-forming derivatives of
these compounds, for example, esters of the acids with
20 lower aliphatic alcohol6, preferably methyl esters, acid
anhydrides or acid halides, and also esters of the
hydroxy compounds with volatile organic acids, for
example, acetates or propionates.
The acids and hydroxy compounds can also be
25 replaced, in whole or in part, by hydroxy acids, each of
which carries at least one hydroxyl group and one acid
group; compounds having in each case one hydroxyl group
and one acid group are preferred.
The starting materials for these polyesters are
30 chosen such that polyesters are obtained which have
hydroxyl numbers (amount of KOH, in mg, equivalent to the
amount of acetic acid bound by l g of resin during
acetylation with acetic anhydride) of from 30 to 200,
preferably from 40 to 150 mg/g, and acid numbers (amount
35 of T~OH, in mg, required to neutralize l g of resin) of
from O to 70, preferably ~rom 2 to 60, and most
preferably from 7 to 50 mg/g. The esterification is
conducted such that these characteristics are obtained.
By adding monof~m~ )n~l aliphatic carboxylic acids, such
~ 218Q8~3
as fatty acids, the acid number can be reduced. This may
be advantageous when nonionic hydrophilic groups are
introduced into the polyester. By introducing dihydroxy
acids, such as dimethylol propionic acid or tartaric
5 acid, the acid number can be increased. The polyesters
are at least partially neutralised with alkali when
dissolved in water.
Suitable precursors for the polyesters include
aliphatic dicarboxylic acids having 2 to 40 carbon atoms,
10 preferably 4 to 36 carbon atoms. Of these compounds, the
linear dicarboxylic acids oxalic acid, malonic acid,
glutaric acid, adipic acid, suberic acid, sebacic acid
and the so-called dimeric fatty acids are preferred.
Examples of suitable branched aliphatic dicarboxylic
15 acids include dimethylsuccinic acid, butylmalonic acid,
diethylmalonic acid, dimethylglutaric acid and
methyladipic acid. Suitable cycloaliphatic dicarboxylic
acids include, for example, hexahydrophthalic,
hexahydroisophthalic and hexahydroterephthalic acid. If
20 desired it is also possible for small proportions (up to
10% of the quantity) of the aliphatic dicarboxylic acids
to be replaced by aromatic dicarboxylic acids. Examples
of compounds suitable for this purpose are the isomeric
phthalic acids, 4,4'-sulfonyldibenzoic acid, 4,4'-di-
25 phenyl ether dicarboxylic acid, and 4,4'-benzophenone-
~1; c~rhn~rylic acid.
Suitable dihydroxy compounds include linear,
branched, or cyclic aliphatic diols having 2 to 40 carbon
atoms, preferably 2 to 20 carbon atoms. Suitable linear
3 o diols include ethylene glycol, 1, 2 - and 1, 3-propylene
glycol, 1, 4-butanediol, 1, 6-hexanediol, the oligomeric
and polymeric polyglycols, such as polyoxyethylene glycol
and polyoxypropylene glycol, mixed polyoxyethyl-
ene/propylene glycols and polyoxybutylene glycol. Also
35 suitable are branched diols, such as neopentylglycol,
2, 2, 4-trimethyl-1, 3-pentanediol, pinacol, and cyclic
diols such as cycl~h~ n~ Lhanol, perhydrobisphenol A,
1, 2- and 1, 4-cyclohexanediol .
-- 218~7~3
Examples of suitable hydroxy acids include lactic
acid, y-hydL~,xybuLyLic acid, o-hydroxyvaleric acid and
~ ydL~xy~aproic acids; these hydroxy acids can also be
employed in the form of the lactones. In small quanti-
ties (such as up to 10 mol/100 mol of the hydroxy acids
or diols and diacids) it is also possible to employ
compounds having one acid group and two or more hydroxyl
groups or else compounds having one hydroxyl group and
two or more acid groups; suitable examples are hydroxy-
succinic acid and dimethylolpropionic acid. By this
means, polyesters branched to a small extent are
obtained .
By employing at least tribasic acids and/or at least
trihydric alcohols, branched polyesters are likewise
obtained. Examples of suitable polybasic acids include
cycloh~xanetricarboxylic acid and butanetetracarboxylic
acid, and examples of suitable polyhydric alcohols
include glycerol, erythritol, pentaerythritol, xylitol
and sorbitol.
Component (B) of the aqueous dispersions according
to the invention comprises acrylate copolymers having
hydroxyl and acid groups. Any such copolymer can be
used. ~lle copolymers generally have a hydroxyl number of
from 40 to 200 mg/g, preferably from 80 to 160 mg/g and
an acid number of from 15 to 50 mg/g. The copolymers are
preferably obtained by free-radical bulk copolymerization
of
(a) from 5 to 40 parts, preferably from 10 to
30 parts, of at least one glycidyl ester of an
o~-branched aliphatic saturated m~nor~rhoxylic
acid,
~b) from 0 to 30 parts, preferably from 5 to
25 parts, of at least one diester of an
(x, ,B -olP ~; n i o;~ 1 1 y ull:,a ~ UL a ted d ica rboxyl ic acid
having 1 to 8 carbon atoms in the ester group,
(c) from 0 to 70 parts, preferably from 5 to
45 parts, of at least one aromatic vinyl
hydrocarbon,
~` 2180~13
(d) from 0 to 60 parts, preferably from 10 to
40 parts, of an alkyl ester of an c~, 3-olefini-
cally unsaturated carboxylic acid, preferably
alkyl or cycloalkyl (meth) acrylates with an
alkyl or cycloalkyl radical having 1 to 18
carbon atoms,
e) from 2 to 47.5 parts, preferably from 5 to
30 parts, of at least one a, ~-olefinically
unsaturated carboxylic acid, preferably
(meth) acrylic acid, the molar quantity of
component (e) always being greater than the
molar quantity of component (a), and
(f) from 5 to 47.5 parts, preferably from 8 to
30 parts, of at least one ~lydLIJx~cllkyl ester
~ of an oL, ~-olefinically unsaturated carboxylic
acid, preferably an ester of (meth) acrylic
acid with polyhydric aliphatic alcohols having
2 to 6 carbon atoms,
the terms "parts" standing for mass fractions, in percent.
In this: ' -;r L, in addition to component (a) it
is necPC~;~ry for in each case one olefinically unsatu-
rated carboxylic acid (e) and a hydroxyalkyl ester of an
unsaturated carboxylic acid (f) to be present in the
copolymerization. It is also possible to employ mixtures
of acrylate copolymers according to (B). The rs of
groups (d), (e), and (f) are referred to below as acrylic
monomers .
For the preparation of the acrylate copolymers it is
possible as component (a) to use glycidyl esters of an
aliphatic saturated monocarboxylic acid having a tertiary
or quaternary carbon atom in the cl position. Particular
preference is given to glycidyl esters of highly branched
monocarboxylic acids with a chain length of 9 to ll
carbon atoms, as are obtainable for example, under the
trade name CARDURA~. In this context, the term "highly
branched" denotes carboxylic acids which have a tertiary
or quaternary carbon atom ad; acent to the carboxyl group .
In the course of the preparation of the acrylate
copolymers, component (a) forms a reaction product with
.-- 2180313
g
component (e), and this product can be free--radically
copolymerized with at least one of components (b), (c),
(d), or (f).
Component (b) comprises diesters of an c(, ~-olefini-
5 cally unsaturated dicarboxylic acid having 1 to 8 carbonatoms in the ester group, preferably maleic and fumaric
esters such as dimethyl maleate, diethyl fumarate,
dibutyl maleate, and dibutyl fumarate.
As component (c) it is possible to employ C~mrollnr9~:
10 such as styrene, o~-methylstyrene and vinylalkylbenzenes
having alkyl radicals of 1 to 3 carbon atoms, for
example, vinyltoluene.
Component (d) comprises alkyl esters of an
c~"~-olefinically unsaturated carboxylic acid, preferably
15 alkyl or cycloalkyl (meth) acrylates with an alkyl or
cycloalkyl radical having l to 18 carbon atoms, examples
being methyl (meth) acrylate, ethyl (meth) acrylate, propyl
(meth) acrylate, butyl (meth) acrylate, hexyl
(meth) acrylate, ethylhexyl (meth) acrylate, lauryl
20 (meth) acrylate, stearyl (meth) acrylate, cyclohexyl
(meth) acrylate, tert-butylcyclohexyl (meth) acrylate,
trimethylcyclohexyl (meth) acrylate, isobornyl
(meth) acrylate and dihydrodicyclopentadienyl
(meth) acrylate. The viscosity-reducing effect, already
25 described in the literature, of rigid bulky ~ ~ such
as isobornyl (meth) acrylate is also evident in the
copolymers using such monomers as (d) according to the
invention .
Suitable components (e) include ~, ~-olefinically
30 unsaturated carboxylic acids such as (meth) acrylic acid,
crotonic acid and monoesters of olefinically unsaturated
rhl~ylic acids whose alcohol ~ ^nt in general has
from 1 to 18 carbon atoms, and unsaturated fatty acids
having 8 to 22 carbon atoms, for example, linolenic acid,
35 linoleic acid, oleic acid, arachidonic acid and r;~;nf~n;~
fatty acid.
As component (f) use is made of ~IydLu~y~lkyl esters
of an ~, ~-olefinically unsaturated carboxylic acid, such
as esters of (meth) acrylic acid with polyhydric aliphatic
~ 2t~Q~3
--10--
alcohols having 2 to 6 carbon atoms. Examples which
may be mentioned include 2-hydroxyethyl (meth) acrylate,
2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl
(meth)acrylate, 2-11ydrvxy}Ju~yl (meth)acrylate, 4-hydroxy-
5 butyl (meth)acrylate, h^Y~n^r~;ol mono(meth)acrylate, andtrimethylolpropane di (meth) acrylate.
The acrylate copolymer dispersions according to the
invention are generally prepared by the method of bulk
polymerization, (but any desired method can be used).
10 The term bulk polymerization refers to a polymerization
which i9 generally carried out without solvents. In some
cases, however, the presence of a solvent in a mass
fraction, based on the final polymer solution, of from 3
to 3596, preferably from 10 to 25%, is also possible.
The polymerization is generally carried out by
initiaIly introducing at least a portion of component
(a), alone or together with at least a portion of
component (b), and, at from 120 to 200C, adding a
mixture of ~ ts (c) to (f) and, if appropriate, any
20 residual components (a) or (b) to be employed, together
with a polymerization initiator and, if desired, with a
regulator, and continuing the bulk polymerization
reaction until a degree of conversion of at least 95%,
preferably of at least 9896, has been reached. In order
25 to prepare an a~iueous dispersion the resulting acrylate
copolymer may be incipiently dissolved first of all with
from 0 to 35 parts, preferably 5 to 25 parts, of a water-
dilutable organic auxiliary solvent, and is then
partially or completely neutralized by adding the
30 corresponding ~uantity of a base. The organic auxiliary
solvent can also be added, in whole or in part, together
with, ^nts (c) to (f). The partially or completely
neutralized acrylate copolymer is then converted into an
a~ueous dispersion by normal or inverse dilution with
35 water. The individual monomers (a) to (f) are in each
case employed in molar o,uantities which are such that the
finished acrylate copolymer has the initially defined
hydroxyl numbers and acid numbers.
2 ~ t ~
--11--
Suitable polymerization initiators include all
customary initiators for free-radical copolymerization,
such as aliphatic azo compounds, for example, azobis[iso-
butyronitrile ] or az obis [ 2 -methy l -butyron itri le ], di acyl
5 peroxides, for example, dibenzoyl peroxide, dialkyl
peroxides, for example, di-tert-butyl peroxide or
di-tert-amyl peroxide, alkyl llydLu~uxides, for example,
tert-butyl hydroperoxide, or peresters, for example,
tert-butyl peroxybenzoate, tèrt-butyl peroxy-
10 2-ethyl h~Y~no~te or tert-amyl peroxy-2-ethylhexanoate.
Preference is given to di-tert-butyl peroxide in a
proportion of from 0 . 5 to 5%, based on the overall mass
of components (a) to (f).
Where it is necessary to employ regulators in order
15 to achieve particularly low average molar masses, use may
be made of alcohols, for example, butanol, or thiols
(mercaptans), for example, dodecanethiol.
Suitable organic auxiliary solvents are, inter alia,
water-dilutable mono- or polyhydric alcohols or glycols,
20 examples being ethanol, n-propanol, isopropanol,
n-butanol, isobutanol, ethylene glycol, diethylene
glycol, triethylene glycol, propylene glycol and
glycerol, water-dilutable monoethers of polyhydric
alcohols, for example, methvxyuLvp~llol or methoxybutanol,
25 and also water-dilutable glycol ethers, for example,
butyl glycol or butyl diglycol.
To neutralize the acid groups it is possible to use
either organic bases or inorganic bases. Preference is
given to the employment of primary, secondary and
30 tertiary amines, for example, ethylamine, propylamine,
dimethylamine, triethylamine, dibutylamine, dimethyl-
isopropylamine, cyclohexylamine, benzylamine, morpholine
and piperidine, and particular preference is given to
amino alcohols such as, for example, N,N-diethylamino-
35 ethanol, N,N-dimethyl-aminoethanol, ethanolamine,
diethanolamine, triethanol-amine, 2-amino-2-methyl-
propanol or 2-dimethylamino-2-methyl-1-propanol. The
neutralization is carried out such that the solutions or
dispersions which result after dilution with water are
- 21~ 3
--12--
stable and generally have a pH of between 6 and lo,
preferably from 7 to 8.5.
The aqueous dispersions are adjusted to a solids
content which is such that they do not become too viscous
5 and remain practicable to handle. They are preferably
adjusted to mass fractions of solids of from 30 to 50%.
From the water-dilutable dispersions of polyacrylate
resins thus obtained, water-dilutable stoving clearcoats
or water-dilutable solid-color stoving topcoats may be
10 produced by generally known methods, by ~lm;x;n~, for
example, an amino resin as cr~cl; nk; n~ agent and, if
desired, customary coatings additives, such as catalysts,
leveling agents and thickeners, rheological A~ ries,
pigments, pigment pastes, antifoams, wetting agents,
15 fillers, light stabilizers, antioxidants, and the like.
Any desired crosslinking agent can be used.
Suitable crosslinking agents in these coating
compositions include reaction products of formaldehyde
with amino resin formers such as urea, alkyleneureas,
20 melamine and gllAnAm;nPC~ or ethers thereof with lower
alcohols, such as methanol or butanol, and also
polyisocyanates and compounds containing anhydride
groups, individually or in combination. In each case the
crosslinking agent is added in a quantity such that the
25 molar ratio of the OH groups of the copolymer to the
reactive groups of the crosslinking agent is preferably
between O . 3 :1 and 3 :1.
Suitable formaldehyde adducts are preferably those
which are derived from urea, r-~lAm;nP and benzog~ nimin~,
30 and also the completely or partially etherified
formaldehyde-amine adducts. With particular preference,
melamine-formaldehyde adducts etherified partially or
completely with aliphatic alcohols having 1 to 4 carbon
atoms are employed as curing agents. Examples of such
35 commercially available hardeners are Maprenal~ MF goo and
VMF 3926 (Hoechst AG) and Cymel~ 303 and 327 (Cytec).
Appropriate mixing proportions are generally in the range
from 50 to 90 parts of copolymer to from 50 to 10 parts
of amine-formaldehyde adduct, based on solid resin.
- 2 ~
--13--
The water-dilutable stoving clearcoats or water-
dilutable solid-color stoving topcoats preferably contain
an amount of amino resin which is such that the mass
ratio of polyacrylate resin to amino resin is from 60:40
to 90:10, particularly preferably from 70:30 to 85:15.
Appropriate formaldehyde-phenol adducts and deriva-
tives thereof can also be employed as hardeners.
In the presence of acids, for example, p-toluene-
sulfonic acid, these crosslinking agents lead to full
curing of the coating. Heat curing can be carried out in
the customary manner at temperatures of from 80 to 200C
in, for example, from 10 to 30 mlnutes.
For curing the products according to the invention,
especially at moderate temperatures or at room tempera-
ture, with cr~ ~cl inkin~ in the context of a two~ nt
coating system, polyisocyanates are particularly
suitable. Suitable polyisocyanate components are in
principle all those aliphatic, cycloaliphatic or aromatic
polyisocyanates which are known from polyurethane
chemistry, individually or in mixtures. Highly suitable
examples include low molar mass polyisocyanates, for
example, hexamethylene diisocyanate, 2, 2, 4- and/or
2, 4, 4-trimethyl-1, 6-hexamethylene diisocyanate,
~lod~ I hylene diisocyanate, tetramethyl-p-xylylene
diisocyanate, 1, 4-diisocyanatocyclohexane, 1-isocyanato-
3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane (IPDI),
2, 4 ' - and/or 4, 4 ' -diisocyanatodicyclohexylmethane, 2, 4 ' -
and/or 4, 4 ' -diisocyanatodiphenylmethane, or mixtures of
these isomers with their higher homologs, as are
obtainable in a manner known per se by phosgenization of
aniline-formaldehyde condensation products, 2,4- and/or
2, 6-diisocyanatotoluene, or any desired mixtures of such
compounds .
It is preferred, however, to employ derivatives of
these simple polyisocyanates as are customary in coatings
technology. These include polyisocyanates having, for
example, biuret groups, uretdione groups, isocyanurate
groups, urethane groups, carbodiimide groups or
allophanate groups, as are described for example, in
2 ~ 80~ ~ ~
,--
--14--
EP O 470 461, which is hereby incorporated by reference.
Particularly preferred modified polyisocyanates include
N,N' ,N"-tris(6-isocyanatohexyl)biuret and its mixtures
with its higher homologs, and also
N,N',N"-tris(6-isocyanatohexyl~isocyanurate and/or its
mixtures with its higher homologs containing more than
one isocyanurate ring.
Crosslinking can be catalyzed by the addition of
organic metal compounds, such as tin compounds and, if
desired, tertiary amines, preferably diethylethanolamine.
Examples of appropriate tin compounds are dibutyltin
dilaurate, dibutyltin diacetate and dibutyltin oxide.
Additional ~ suitable for curing at elevated
temperature are capped polyisocyanates, polycarboxylic
acids, and/or their anhydrides.
Prior to application, the water-dilutable coating
materials formulated with the water-dilutable poly-
acrylate resin dispersions according to the invention are
generally adjusted to spray viscosity -- in general a flow
time of from 20 to 40 s from the DIN 4 cup (DIN 53 211)
-- and to a pH of from 7 to 9.
The water-dilutable coating materials formulated
with the dispersions according to the invention have a
solids content at spray viscosity, with a relatively low
proportion of organic auxiliary solvents, which is such
that just one spray pass leads to coating films of
sufficient thir.kn~cc (the thickness of the cured coating
film should preferably be between 30 and 65 ,~m), which
after curing (for example, stoving, force drying) give
nonyellowing films of good appearance which are free from
boil marks and have high levels of resistance"~c:p~r~lly
to sulfuric acid, xylene, and acetone.
The water-dilutable stoving clearcoats formulated
with the dispersions according to the invention are
particularly suitable for the production of metallic
finishes by the basecoat/clearcoat method.
One advantage of the acrylate copolymers is that it
is not necessary to distil off any solvents whatsoever
during the preparation and that water-dilutable binders
.. , ..... ,,,,, _ _
` ~ 2180813
--15--
with low weight average molar masses ~, of, for example,
about 3,000 g/mol, preferably about 3,500 g/mol, and
particularly preferably about 4,000 g/mol, can be
prepared without the addition of regulators. The upper
limit for the ~, usually is about 100, 000 g/mol, at least
80,000 g/mol, preferably at least 70,000 g/mol. This
results in binders having a high solids content and a low
proportion of organic auxiliary solvents.
One advantage of the dispersions over known water-
dilutable binders is the extremely high resistance of the
water-dilutable coating materials formulated therewith
with respect to inorganic acids, especially sulfuric
acid. The sulfuric acid resistance of the water-
dilutable coating materials, which is used as a test for
the resistance to environmental influences such as acid
rain, is in many cases where the binders according to the
invention are used even better than that of conventional
coating materials. In stoving enamels, in combination
with highly reactive partially etherified r-lAm;n~-
formaldehyde resins, extremely good resistance to organic
agents such as xylene and acetone is found, which goes
far beyond that of conventional coating systems. A
further advantage of the binders according to the
invention is their high yellowing stability when used in
one-component stoving enamels in combination with amino
resins .
It is noted that the stoving enamels produced with
the dispersions according to this invention, without the
addition of fluorinated c~ described in
DE-A 40 27 594 and without free or capped
polyisocyanates, are highly stable to water. This
constitutes an ecological advantage.
The invention is illustrated by the following non-
limiting examples. In the examples which follow all
parts are by mass and all percentages (%) are mass
fractions in g/100 g, unless specified otherwise.
~ 2~sa6~
Examples
1) Preparation of a hydrophilic polyester A
493.3 g of adipic acid (3.45 mol), 541.4 g of
pimelic acid (3.38 mol), 450.2 g of 1~6-h~y~ne~liol
(3.81 mol; as 529.6 g of an 85% strength solution in
water) and 297.8 g of neopentylglycol (2.86 mol; as
330.9 g of a 90% strength solution in water) are placed
in a 5 1 vessel, 8 . 2 g of dibutyltin oxide are added as
catalyst, and then the components are melted together,
during which the water is distilled off. ~ieating is
continued to 190C under a cloud of nitrogen. The
mixture is stirred at 190C until the cloudiness
disappears. The acid number (AN = mKOH/mresin) of the
condensation product is about 45 mg/g. The resin is
cooled to about 110C and 215.2 g (1.60 mol) of
dimethylolpropionic acid are metered in under nitrogen.
The mixture is again heated to 190 to 200C under
nitrogen and is held at this temperature until the acid
number has again reached about 45 mg/g. The batch is
then cooled to about 70C. A sample of the resin shows
a hydroxyl number (OHN = m~O~/mre~ln) of 83 mg/g,
a viscosity (measured on a 50% strength solution in
n-butanol in an Ubbelohde viscometer at 23C) of
4, 050 mPa s and an iodine color number of below 2 . The
resin is diluted with n-butanol at 70C to a solids
content by mass of 90%. By adding dimethylaminoethanol
with stirring at about 80C, the diluted resin is
adjusted to a degree of neutralization of 80%, and then
diluted with deionized water at 30C to a solids content
by mass of 45%.
2 ) Preparation of a hydrophilic polyester B
In accordance with the method of Example 1, 657 . 7 g
of adipic acid and 485 . 4 g of sebacic acid are melted
together with 425.5 g of 1~6-h~y~nf~;ol~ 297.2 g of
diethylene glycol and 26.8 g of trimethylolpropane and
the mixture is stirred at 190C until the acid number has
reached a constant value of about 15 mg/g. The mixture
218~3
--17--
is cooled, 180 g of dimethylolpropionic acid are added,
and c~nfl~n~ation is continued until the acid number
remains constant. After cooling, the resin is taken up
in 183 g of n-butanol to give a solids content by mass of
5 90%. Dimethylaminoethanol is used to adjust the batch to
a degree of neutralization of 70%, after which it is
diluted with deionized water to a solids content by mass
of 45%.
3 ) Preparation of an acrylate resin C
358 . 6 g of Cardura~ E10 (glycidyl ester of
neodecanoic acid~ are charged to a vessel with reflux
.-,.nfl~ncor and stirrer and are heated to 160C. A monomer
mixture consisting of 348.6 g of styrene, 263.4 g of
methyl methacrylate, 286 . 6 g of hydroxypropyl
15 methacrylate and 175 . 6 g of acrylic acid dissolved in
226.6 g of n-butanol, with the addition of 26.4 g of
tert-butyl peroxy-2-ethyl h~ nnate as free-radical
initiator, is metered in at a uniform rate over the
course of 6 hours. On reflux the temperature becomes
20 established at about 135C. After a post-reaction time
of two hours the mixture is cooled to 90*C and then the
polyester A (314.2 g of the 459~ strength solution) is
added. The product has a solids content of 77% and an OH
number of about 130 mg/g. N,N-dimethylaminoethanol is
25 used at BO to 90C to adjust the degree of neutralization
to 65%, and then at a temperature above 60C a quantity
of deionized water is added which reduces the solids
content by mass to 40%. The mean particle size of this
dispersion is about 200 nm.
30 4) Preparation of an acrylat~ re~in D
358 . 6 g of Cardura~ E10 (glycidyl ester of
neodecanoic acid) are charged to a vessel with reflux
~-r~nflGnc~or and stirrer and are heated to 160C. A monomer
mixture consisting of 348 . 6 g of styrene, 263 . 4 g of
35 methyl methacrylate, 286 . 6 g of hydroxypropyl
methacrylate and 175. 6 g of acrylic acid dissolved in
226.6 g of n-butanol, with the addition of 26.4 g of
2~8~3
.--
--18--
tert-butyl peroxy-2-ethylhexanoate as free-radical
initiator, is metered in at a uniform rate over the
course of 6 hours. On reflux the temperature becomes
established at about 135C. After a post-reaction time
5 of two hours the mixture is cooled to 90C and then the
polyester B (314 . 2 g of the 45% strength solution) is
added. The product has a solids content of 77% and an OH
number of about 130 mg/g. N,N-dimethylaminoethanol is
used at 80 to 90C to adjust the degree of neutralization
10 to 65%, and then at a temperature above 60C a quantity
of deionized water is added which reduces the solids
content by mass to 40%. The mean particle size of this
dispersion is about 200 nm.
5) Preparation of an agueous t.~. o ~. ~on~nt clearcoat
from a commercial acrylic re~in (control)
80. 6 parts of a commercial agueous acrylate resin
dispersion (Macrynal0 VSM 2521) having a hydroxyl number
of 140 mg/g and a solids content by mass of 42% are taken
as initial charge; 1. 9 parts of an etherif ied melamine-
20 formaldehyde resin (Maprenal~ MF 920) diluted with9 . 9 parts of deionized water are added thereto.
4 . 6 parts of a mixture of solvents (Proglyde~ DMM
dipropylene glycol dimethyl ether, Dowanol~D DPnB =
dipropylene glycol n-butyl ether, MPA = methuxy~ yl
25 acetate in a ratio of 2 :1:1) are used to dissolve 3 parts
of additives (antifoams and light stabilizers) and this
solution is added.
loO parts of this binder mixture are mixed with
20 parts of an 80% strength solution of a commercial
30 isocyanate (Desmodur~ N 3400) in Proglyde DMM, and the
mixture is subsequently ad~usted with deionized water to
a spray viscosity corresponding to a flow time of
25 seconds from a cup (according to DIN 53 211 at 23C).
2180~13
--19--
6~ Preparation of an aqueou3;, _ --,t clearcoat
from the acrylic resin c
80. 6 parts of the aqueous acrylate resin dispersion
from Example 3 having a hydroxyl number of 130 mg/g and
5 a solids content by mass of 40% are taken as initial
charge; 1.9 parts of an etherified melamine-formaldehyde
resin (Maprenal1~ MF 920) diluted with 9.9 parts of
deionized water are added thereto. 4. 6 parts of a
mixture of solvents (Proglyde~ DMM = dipropylene glycol
10 dimethyl ether, Dowanol~ DPnB = dipropylene glycol
n-butyl ether, MPA = methoxypropyl acetate in a ratio of
2 :1: 1) are used to dissolve 3 parts of additives
(antifoams and light stabilizers) and this solution is
added .
100 parts of this binder mixture are mixed with
20 parts of an 80% strength solution of a commercial
isocyanate (Desmodur N 3400) in Proglyde DMM, and the
mixture is subsequently adjusted with deionized water to
a spray viscosity corresponding to a flow time of
seconds from a cup (according to DIN 53 211 at 23C).
7) Preparation of an aqueous t ~.O ~ _ ant clearcoat
from the acrylic resin D
The procedure of Example 6 is repeated but using the
aqueous acrylate resin dispersion from Example 4.
25 8) Preparation of an agueous ~ t clearcoat
from a commercial acrylic resin (control)
The procedure of Example 5 is repeated but using,
instead of the isocyanate employed therein, 37.5 parts of
isophorone diisocyanate as a 70% strength solution in a
30 mixture of xylene and methu,~y~Lu~yl acetate.
9 ) Preparation of an aqueous two-- _ncnt clearcoat
from the acrylic resin c
The procedure of Example 6 is repeated but using,
instead of the isocyanate employed therein, 37.5 parts of
35 isophorone diisocyanate as a 70% strength solution in a
mixture of xylene and methoxypropyl acetate.
2180~13
--20--
10) Performance tes~ing o~ the clearcoats
The two-component clearcoats from Examples 6 to 9
were tested in comparison with a commercial, solvent-
containing nr~n~ system (Macrynal~ SM 510 n/Desmodur
5 N 75). The results are summarized in the ta'ole.
2 1 8 (~ 3
r~ ~
,, w o r o
X V ~ ~D
~D` ` ` ~D o ~
W ,"
8 -- ~
~ o ~ o r o o
.r .a
,W o r~ O o
~O
N ,~
U~ O ~D o o
.1 ' ~ ~ O ~ ~
O .,1 0 ~ O
.~ ~ ~ O .,~ O a~ O o
V ~ E ~;
~ U iU ~
r~ ~ r
~ X .- Li r~ U U L
L E ' ~ I X L ~ IJ ... _ _
_ . . . . . _ .
2 ~ t: s
--22--
It is evident that the properties of the externally
emulsified systems (Examples 6 and 9) are equal to those
of the auto-emulsified system (Examples 5 and 8).
Nhereas with the autoemulsified system coat thicknesses
5 of not more than about 40 ~Lm can be applied in one pass
without surface defects resulting, with the externally
emulsified system according to the invention it is
possible to apply coats up to 65 mm thick in one
operation without ~he occurrence of surface defects (in
10 the form of so-called boil marks). The resistance to
chemicals (16 hours' exposure to anticorrosion agents;
30 minute6 ' exposure each to 3796 strength sulfuric acid,
1% strength sodium hydroxide solution, brake fluid, tar
test solution; so-called cation-anion test) does not
15 differ for the tested coatings in the respective
thickness indicated.
AIthough only a few exemplary embodiments of this
invention have been described in detail above, those
skilled in the art will readily appreciate that many
20 modifications are possible in the exemplary ~mho~;r~nts
without materially departing from the novel ~ h;n~c and
advantages of this invention. Accordingly, all such
modifications are intended to be included within the
scope of this invention.
